Loudspeaker

ABSTRACT

The present invention is directed to a speaker using lightweight, highly rigid diaphragm having excellent frequency characteristic and improving resistance to environment (including resistance to UV and resistance to fading). For this end, the speaker utilizes a cone-shaped diaphragm made from foamed or cellular resin such as polyethylene terephthalate (PET) resin or polyethylene naphthalate (PEN) resin with 30 μm average cell size. The use of such cone-shaped diaphragm is effective to improve sound quality of the speaker.

FIELD OF INVENTION

The present invention relates generally to a speaker, more specificallyto a speaker using light weight, highly rigid cone-shaped diaphragm toprovide excellent frequency response.

BACKGROUND OF INVENTION

In conventional speakers, paper pulp, metal, polypropylene, etc. arenormally used as the diaphragm.

These conventional diaphragms have various drawbacks. Those madeprimarily from paper pulp are not moisture-resistant, fade under normalenvironment and degrade in aging. Those made from metal are hard on thesurfaces and have high Young's modulus of elasticity but encounterharmonic distortion due to split vibrations and poor processability suchas adhesiveness. Those made of synthetic resin such as polypropylene(PP) or formed polyethylene are low density, poor rigidity and poorheat-resistant.

DISCLOSURE OF THE INVENTION

In order to overcome these drawbacks, the speaker according to thepresent invention features in constructing a cone-shaped diaphragm madefrom thermoplastic resin such as polyethylene terephthalate resin (PET)or polyethylene naphthalate resin (PEN) with ultra micro foam of 30micron or less in average cell size. Such cone-shaped diaphragm is lightweight, provides large internal loss, is excellent in rigidity (high inacoustic speed) and provides excellent sound quality.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a longitudinal cross-section view of the speaker according toa first embodiment of the present invention:

FIG. 2 is a microscopic photograph in cross-section of the diaphragm ofthe primary portion of the speaker according to the present invention;

FIG. 3 shows frequency response characteristics of the speaker accordingto the first embodiment of the present invention using a diaphragm madefrom PET;

FIG. 4 is a longitudinal cross-section view of the speaker according tothe second embodiment of the present invention; and

FIG. 5 is a characteristic curve showing the spectral reflection of thecone-shaped diaphragm to be used in the speaker of the presentinvention.

PREFERRED EMBODIMENTS OF THE INVENTION First Embodiment

Now, a first embodiment of the speaker according to the presentinvention will be described by reference to FIGS. 1 and 2.

As illustrated in FIG. 1, the speaker 1 according to the presentinvention comprises a magnetic circuit 2 including a magnet 7 and acenter magnetic pole 22 having a ring-shaped magnetic gap 21, a cover 9for firmly holding outside the magnetic circuit 2, a voice coil 3disposed in the ring-shaped magnetic gap 21, a damper 4 disposed betweenthe voice coil bobbin 31 for the voice coil 3 and a frame 6 for holdingthe voice coil 3 in the ring-shaped magnetic gap 21 and a cone-shapeddiaphragm 5 adhered to the edge of the voice coil bobbin 31 and havingan outer periphery adhered to the inner periphery of the edge 51. Theedge 51 is then adhered to the outer edge portion of the frame 6.

Now, the cone-shaped diaphragm 5 will be described in detail hereunder.The cone-shaped diaphragm 5 is made from foamed polyethyleneterephthalate (PET) commercially available from Furukawa ElectricIndustries under the trademark of “MCPET” or foamed polyethylenenaphthalate (PEN).

As apparent from the microscopic photograph in cross-section of thecone-shaped diaphragm, the diaphragm made from PET in the embodimentaccording to the present invention has small cells. Illustrated at thebottom in FIG. 2 is a scale of 11 dots having 3 micron gap betweenadjacent dots.

Illustrated in Table 1 below is comparison of various characteristics ofthe speaker utilizing the cone-shaped diaphragms according to thepresent invention and speakers utilizing diaphragms made fromconventional materials. The speakers are 16 cm in diameter.

TABLE 1 present present reference reference speaker speaker speakerspeaker using PET using PEN using PP using paper diaphragm diaphragmdiaphragm pulp diaphragm density 0.25~0.35 0.33 1.15~1.20 0.7~0.8 extentof 3.8~5.4 4 foaming thickness 0.85 0.60 0.35 0.35~0.4  (mm) average 2010 cell diameter (μm) weight 2.3 2.0 4.5 2.3 (g/mm{circumflex over( )}2) acoustic 1850 2050 1800 1600 speed (m/s) tan δ 0.040 0.06 0.0650.035 resistance no change no change fade easy to fade to UV Notes (1)light weight and thick, less split vibrations to cause less distortion.(2) light weight and thick. less split vibrations to cause lessdistortion. (3) larger tan δ and less distortion but heavy and lesssound pressure as a speaker. (4) high sound pressure as a speaker andlarger distortion. Poor appearance.

In fabrication process of the cone-shaped diaphragm in Table 1, anattempt was made to make a diaphragm of PET with 500 μm average celldiameter. However, rigidity (acoustic speed) was significantly low andcharacteristics as the diaphragm for speaker were inferior to those ofthe reference speakers in Table 1.

This leads to a conclusion that simple foaming of resin is not usable asa speaker diaphragm. Table 1 proves that a speaker using a cone-shapeddiaphragm made from resin having ultra micro foaming of 30 μm or lessaverage cell size is lighter and high rigid to provide excellent speakercharacteristics.

As apparent from the reference value in Table 1, the speaker using aconventional diaphragm made from paper pulp has smaller tan δ, largerdistortion and poor appearance quality. On the other hand, the diaphragmmade from PP has larger tan δ, smaller distortion, larger weight andlower reproduced sound pressure of the speaker.

Illustrated in FIG. 3 are frequency characteristic curves of thespeakers using a diaphragm made from PET according to the presentinvention. {circle around (1)} is the sound pressure frequencycharacteristic of the speaker on the center axis (0°). {circle around(2)} is the frequency characteristic of the second harmonic distortion.{circle around (3)} is the frequency characteristic of the thirdharmonic distortion. {circle around (4)} is the impedance characteristicof the voice coil. Although not shown in FIG. 3, the speaker accordingto the present invention is 1.5 dB higher in average in the soundpressure frequency response and exhibits less second and third harmonicsas compared to the reference speaker.

It is assumed that the use of foamed resin of 30 μm or smaller cell sizeis responsible for obtaining the light weight, highly rigid cone-shapeddiaphragm.

Since the diaphragm according to the present invention can be usedexactly the same manner as the conventional diaphragms, it isunnecessary to modify any step of making speakers. It is possible toobtain uniform quality and improve sound quality.

Second Embodiment

Now, the second embodiment of the speaker according to the presentinvention will be described by reference to FIG. 4. In FIG. 4, elementsidentical to those in the first embodiment as illustrated in FIG. 1 arerepresented by identical reference numerals.

As illustrated in FIG. 4, the speaker 1 comprises a magnetic circuit 2having a center magnetic pole 22, a cylindrical support 8 mounted ontothe base of the center magnetic pole 22, an induction coil 81 mounted onthe middle portion of the support 8 with a certain gap from the voicecoil bobbin 31 and an LED holder 83 disposed at the end of the support8. The LED holder 83 is designed to radially hold a plurality of LEDs 82so that light is emitted through respective openings onto the surface ofthe cone-shaped diaphragm 5.

The cone-shaped diaphragm 5 is identical to the cone-shaped diaphragm ofthe first embodiment and made from foamed PET with 30 μm or smalleraverage cell size.

Illustrated in FIG. 5 is a characteristic curve showing spectralreflection on the surface of the cone-shaped diaphragm used in thesecond embodiment. It is apparent from FIG. 5 that the reflectioncharacteristic is very good over the entire zone of visible rays.

By using the cone-shaped diaphragm made from foamed resin with 30 μm orsmaller average cell size, the diaphragm becomes highly rigid and thusproviding an excellent speaker. Also, the use of 30 μm or smalleraverage cell size is effective to provide the cone-shaped diaphragm ofexcellent reflectance, thereby enabling to provide a speaker withenhanced visual interest.

When an audio signal is applied to the voice coil of the speaker 1, thevoice coil 3 vibrates in the magnetic gap 21. Such vibration istransferred to the cone-shaped diaphragm 5 to generate audio sound. Atthis time, the vibration of the voice coil 3 develops magnetic flux andmagnetic field in the magnetic gap 21. The induction coil 81 woundaround the voice coil bobbin 31 with a space intersects with theinductive magnetic field to induce an inductive current in the inductivecoil 82. The induced voltage is 2˜3 volts and is used (after necessaryamplification) to turn on and off the LEDs 82.

In the above configuration, LEDs 82 are controlled to selectively emitdifferent colored light such as blue, red, yellow, etc. in response tothe vibration magnitude of the voice coil 3 of the speaker 1. LEDs 82are disposed near the surface of the diaphragm 5 in an orientation toilluminate the diaphragm 5. Since the diaphragm 5 has excellent spectralcharacteristic, almost all light from LEDs 82 is total reflected toilluminate a large area of the cone-shaped diaphragm 5 in response tohigh/low or strong/weak of the reproduced sound. This arrangement iseffective to entertain the listeners visually in addition to the audio.

INDUSTRIAL APPLICABILITY

As apparent from the above description, the speaker according to thepresent invention features in using the cone-shaped diaphragm made fromthermoplastic resin such as polyethylene terephthalate (PET) resin orpolyethylene naphthalate PEN) resin with ultra micro foam of 30 μm orsmaller average cell size. The diaphragm is light and yet has largerinternal loss and excellent rigidity (fast acoustic speed) to providethe speaker having excellent sound quality.

Also, the speaker comprises the cylindrical support at the base of thecenter magnetic pole of the magnetic circuit, the induction coil woundaround the support at the middle portion separating from the voice coiland a plurality of LEDs radially disposed in the LED holder secured tothe end of the support. The LEDs are selectively turned on or off inresponse to the driving of the voice coil bobbin of the speaker. Thecone-shaped diaphragm is made from formed resin of 30 μm or smalleraverage cell size. In this arrangement, the surface of the diaphragm hasimproved spectral reflectance to provide visual entertainment.

1. A speaker comprising: a magnetic circuit having a center magneticpole and an air gap; a voice coil wound around a voice coil bobbindisposed in the air gap of the magnetic circuit; a frame mounted ontothe magnetic circuit; a cone-shaped diaphragm made from foamed resin anddisposed between the frame and the one end of the voice coil bobbin; asupport mounted on the center magnetic pole of the magnetic circuitincluding an induction coil wound around the support; and at least onelight source held in a holder secured to the end of the support fordirecting light onto the cone-shaped diaphragm by being energized by thevoltage induced in the induction coil.
 2. A speaker of claim 1, whereinthe holder is configured to hold a plurality of light emitting diodes(LEDs) directed to illuminate the cone-shaped diaphragm in radialmanner.
 3. A speaker of claim 1, wherein the light source is controlledto emit light of different color depending on the audio signal to beapplied to the voice coil.
 4. A speaker of claim 2, wherein the lightsource is controlled to emit light of different color depending on theaudio signal to be applied to the voice coil.